1. Field of the Invention
This invention relates to an at least partially implantable hearing system comprising at least one electromechanical output transducer and a micromanipulator for positioning the transducer and for fixing the transducer in a position set by the micromanipulator, the micromanipulator being adapted to be fixedly attached by fixing means to a cranial vault.
2. Description of Related Art
The expression “at least partially implantable hearing system” is defined here as a system in which a sound signal is picked up by at least one sensor which transduces a sound signal into an electrical signal (microphone function), in which this electrical signal is electronically further processed and amplified, and in which an output signal of the system causes an electromechanical stimulation of the damaged hearing, wherein at least one component of the system, particularly the electromechanical output transducer, is designed for being implanted.
The expression “hearing dsefder disorder” is defined here as including any type of inner ear and middle ear damage, any combined inner ear and middle ear damage, and a temporary or permanent noise impression (tinnitus).
Hearing systems of the presently considered type usually comprise at least one acoustic sensor (microphone) for picking up acoustic signals and converting them into electrical audio sensor signals, an electronic signal processing unit for audio signal processing and amplification, an electrical power supply unit which supplies individual components of the system with energy, and an electromechanically actoric output arrangement including at least one electromechanical transducer for stimulation of the middle and/or inner ear. This transducer is connected to a mechanical positioning and fixing system which here is termed “micromanipulator” and which is fixedly and permanently attached to the cranial vault. In the case of a fully implantable hearing system in which the implant is provided with a secondary storage element for electrical energy, the system further comprises a wireless transcutaneoiis charging device.
Electronic measures for rehabilitation of inner ear damage which cannot be cured by surgery have currently achieved great importance. With total failure of the inner ear, cochlear implants with direct electrical stimulation of the remaining auditory nerves are in routine clinical use. For medium to severe inner ear damage, for the first time, fully digital hearing devices are presently being used which open up a new world of electronic audio signal processing and offer expanded possibilities of controlled audiological fine tuning of the hearing devices to the individual inner ear damage. In spite of major improvements of hearing aid hardware achieved in recent years, in conventional hearing aids, there remain basic defects which are caused by the principle of acoustic amplification, i.e. especially by the reconversion of the electronically amplified signals into airborne sound. These defects include aspects such as the visibility of the hearing aids, poor sound quality as a result of electromagnetic transducers (speakers), closed external auditory canal as well as feedback effects at high acoustic gain.
As a result of these fundamental defects, there has long been the desire to move away from conventional hearing aids with acoustic stimulation of the damaged inner ear and to replace them by partially or fully implantable hearing systems with direct mechanical stimulation. Implantable hearing systems differ from conventional hearing aids: the acoustic signal is converted with a proper microphone into an electrical signal and amplified in an electronic signal processing stage; this amplified electrical signal, however, is not sent to an electroacoustical transducer (speaker), but rather to an implanted electromechanical transducer providing for output-side mechanical vibrations which are sent directly, and therefore with direct mechanical contact, to the middle ear or inner ear, or indirectly via an air gap in, for example, electromagnetic converter systems. This principle applies regardless of whether implantation of all necessary system elements is partial or complete and also regardless of whether an individual with pure inner ear impairment with a completely intact middle ear or an individual with combined hearing impairment, in which the middle and inner ear is damaged, is to be rehabilitated. Therefore implantable electromechanical transducers and methods for coupling the mechanical transducer vibrations to the functioning middle ear or directly to the inner ear for rehabilitation of a pure inner ear impairment, or to a remaining ossicle of the middle ear in the case of an artificially or pathologically altered middle ear for taking care of a hearing disorder caused by a disturbance of sound conduction, or for combinations of such disorders, have been described in the recent scientific literature and in many patents.
Useful electromechanical transducer processes include basically all physical transducer principles, such as electromagnetic, electrodynamic, magnetostrictive, dielectric and piezoelectric. Various research groups, in recent years, have focused essentially on two of these processes, namely electromagnetic and piezoelectric processes. A survey can be found in H. P. ZENNER and H. LEYSIEFFER (HNO 10/1997, vol. 45, pp. 749–774).
In the piezoelectric process, direct mechanical coupling of the output-side transducer vibrations to the middle ear ossicle or to the oval window is essential. In the electromagnetic principle, force coupling between the transducer and ossicle, on the one hand, can take place “without contact”, i.e. via an air gap; in this case, only the permanent magnet is caused to vibrate by the transducer being in direct mechanical contact with the middle ear ossicle by permanent fixation. On the other hand, it is possible to implement the transducer entirely in a housing (in this case the coil and the magnet preferably being coupled with the smallest possible air gap) and to transmit the output-side vibrations via a mechanically stiff coupling element with direct contact to the middle ear ossicle (see FREDRICKSON et al.: Ongoing investigations into an implantable electromagnetic hearing aid for moderate to severe sensorineural hearing loss; Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 107–121; and H. Leysieffer et al., HNO 10/97, vol. 45, pp. 792–800).
The patent literature contains some of the aforementioned versions of both electromagnetic and also piezoelectric hearing aid transducers: U.S. Pat. No. 3,712,962, EPLEY; U.S. Pat. No. 3,870,832, FREDRICKSON; U.S. Pat. No. 3,882,285, NUNLEY et al.; U.S. Pat. No. 4,850,962, SCHAEFER; U.S. Pat. No. 5,015,224, MANIGLIA; U.S. Pat. No. 5,277,694, LEYSIEFFER et al.; U.S. Pat. No. 5,554,096, BALL; U.S. Pat. No. 5,707,338, ADAMS et al.; U.S. Pat. No. 6,123,660, LEYSIEFFER; U.S. Pat. No. 6,162,169, LEYSIEFFER; International Patent Application Publications WO-A 98/06235, ADAMS et al.; WO-A 98/06238, ADAMS et al.; WO-A 98/06236, KROLL et al.; WO-A 98/06237, BUSHEK et al.
The partially implantable piezoelectric hearing system of the Japanese group of Suzuki and Yanigahara presupposes, for implantation of the transducer, the absence of the middle ear ossicles and a free tympanic cavity to be able to couple the piezo element to the stapes (Yanigahara et al.: Efficacy of the partially implantable middle ear implant in middle and inner ear disorders: Adv. Audiol., Vol. 4, Karger Basel (1988), pp. 149–159; Suzuki et al.: Implantation of partially implantable middle ear implant and the indication. Adv. Audiol., Vol. 4, Karger Basel (1988), pp. 160–166). Likewise, in the method of implanting a hearing system for inner ear hearing-impaired according to SCHAEFER (U.S. Pat. No. 4,850,962) basically the incus is removed in order to be able to couple a piezoelectric transducer element to the stapes. This also applies to further developments which are based on the SCHAEFER technology and which are described in the above mentioned patents (U.S. Pat. No. 5,707,338, ADAMS et al.; International Patent Application Publications WO-A 98/06235, ADAMS et al.; WO-A 98/06238, ADAMS et al.; WO-A 98/06236, KROLL et al.; WO-A 98/06237, BUSHEK et al.).
The BALL electromagnetic transducer (“Floating Mass Transducer FMT” of U.S. Pat. No. 5,554,096, BALL; U.S. Pat. No. 5,624,376, BALL et al.) is, on the other hand, directly fixed to the long process of the incus when the middle ear is intact. The electromagnetic transducer of the partially implantable system of FREDRICKSON (Fredrickson et al.: Ongoing investigations into an implantable electromagnetic hearing aid for moderate to severe sensorineural hearing loss, Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 107–121) is directly mechanically coupled to the body of the body of the incus when the ossicular chain of the middle ear is likewise intact. The same applies to the piezoelectric transducers of LEYSIEFFER (LEYSIEFFER et al.: An implantable piezoelectric hearing aid converter for the inner ear hearing-impaired. HNO 1997/45, pp. 792–800; U.S. Pat. No. 5,277,694, LEYSIEFFER et al.; U.S. Pat. No. 6,123,660, LEYSIEFFER; U.S. Pat. No. 6,162,169, LEYSIEFFER). Also in the electromagnetic transducer system of MANIGLIA (MANIGLIA et al.: Contactless semi-implantable electromagnetic middle ear device for the treatment of sensorineural hearing loss, Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 121–141) with the ossicular chain intact a permanent magnet is permanently mechanically fixed to the ossicular chain, but is mechanically driven via an air gap coupling by a coil.
In the described transducer and coupling versions, basically, two implantation principles can be distinguished:    a) In the case of the one principle the electromechanical transducer with its active transducer element is located itself in the middle ear region in the tympanic cavity and the transducer is directly connected there to an ossicle or to the inner ear (U.S. Pat. Nos. 4,850,962, 5,015,225, 5,707,338, 5,624,376, 5,554,096, and International Patent Application publication Nos. WO 98/06235, WO 98/06238, WO 98/06236, and WO 98/06237).    b) In the other principle the electromagnetic transducer with its active transducer element is located outside of the middle ear region in an artificially formed mastoid cavity; the output-side mechanical vibrations are then transmitted to the middle or inner ear by means of mechanically passive coupling elements via suitable surgical accesses (the natural aditus ad antrum (U.S. Pat. No. 6,077,215), opening of the chorda-facialis angle or via an artificial hole from the mastoid (Fredrickson et al.: Ongoing investigations into an implantable electromagnetic hearing aid for moderate to severe sensorineural hearing loss. Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 107–121; U.S. Pat. No. 5,277,694; U.S. Pat. No. 6,123,660; U.S. Pat. No. 6,162,169). This type of access requires an implantable positioning and fixing system (micromanipulator) for “suspending” the electromagnetic transducer, wherein the positioning and fixing system is to be fixedly and durably attached to the skull (U.S. Pat. No. 5,788,711 and commonly owned U.S. patent application Ser. No. 09/468,853).
An advantage of the a) type versions is, that the transducer can be made as a so-called “floating mass” transducer, i.e., the transducer element does not require any “reaction” via secure screwing to the skull bone, but it vibrates based on the laws of mass inertia with its transducer housing and transmits these vibrations directly to a middle ear ossicle (U.S. Pat. Nos. 5,624,376, 5,554,096, and 5,707,338, and International Patent Application publication no. WO 98/06236). On the one hand, this means that an implantable fixation system on the cranial vault can be advantageously omitted; on the other hand, this version disadvantageously means that bulky artificial elements must be placed in the tympanic cavity, and their long-term stability and biostability are currently not known or guaranteed, especially in the case of temporary pathological changes of the middle ear (for example, otitis media). Another major disadvantage is that the transducer together with its electrical supply line has to be transferred from the mastoid into the middle ear and must be fixed there using suitable surgical tools; this requires an expanded access through the chorda facialis angle, and thus, entails a latent hazard to the facial nerve which is located in the immediate vicinity. Furthermore, such “floating mass” transducers can be used merely in a very limited manner or not at all, when the inner ear is to be directly stimulated for example via the oval window, or when, due to pathological changes, for example the incus is substantially damaged or is no longer present, so that such a transducer no longer can be mechanically connected to an ossicle that is able to vibrate and is in connection with the inner ear.
A certain disadvantage of the transducer versions as per b) is that the transducer housing is to be attached to the cranial vault with the aid of implantable positioning and fixation systems (micromanipulators) (advantageous embodiment U.S. Pat. No. 5,788,711). A further disadvantage of the transducer versions as per b) is that a recess is to be made, preferably by an appropriate laser, in the respective ossicle in order to allow the application of the coupling element. This, on the one hand, is technically complicated and expensive and, on the other hand, involves risks for the patient. Both in the partially implantable system of FREDRICKSON ( “Ongoing investigations into an implantable electromagnetic hearing aid for moderate to severe sensorineural hearing loss”, Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 107–121) as well as in the fully implantable hearing system of LEYSIEFFER and ZENNER (HNO 1998, vol. 46, 853–863 and 844–852), when the vibrating transducer part is coupled to the body of the incus, it is assumed that for permanent and mechanically secure vibration transmission the tip of the coupling rod which is placed in the laser-induced depression of the middle ear ossicle undergoes osseointegration over the long term, i.e., the coupling rod coalesces solidly with the ossicle and thus ensures reliable transmission of dynamic compressive and tensile forces. However, this long-term effect is currently not yet scientifically proven or certain. Furthermore, in this type of coupling, in case of a technical transducer defect, there is the disadvantage that decoupling from the ossicle to remove the transducer can only be done with mechanically based surgical methods; this can mean considerable hazard to the middle ear and especially the inner ear. Therefore further coupling elements, partly involving novel surgical access paths, were developed which minimize or no longer have the above mentioned disadvantages (U.S. Pat. No. 5,941,814, LEHNER et al., commonly owned U.S. patent applications Ser. Nos. 09/576,009; 09/613,560; 09/626,745; 09/680,489).
The major advantages of these converter embodiments as per b), however, are that the middle ear remains largely free, and that access to the middle and inner ear can take place in a manner which permits, when using a properly designed micromanipulator, reaching of basically any point of the middle ear or of the inner ear, respectively, as stimulation site. One preferable surgical process for this purpose is described in U.S. Pat. No. 6,077,215, LEYSIEFFER. This results in the further advantage that basically all combinations of middle and inner ear damages can be attended, and that a pure inner ear stimulation likewise is possible via a direct access, for example an artificial window, and by using proper coupling elements. In this connection a detachable interconnection between transducer and coupling element has been disclosed in commonly owned U.S. patent application Ser. No. 09/680,489.
In a hearing system known from International Patent Application Publication WO 00/48426 a unit consisting of an actoric electromechanical transducer and of a positioning and fixation system (here called “micromanipulator”) is detachably connected to mounting means fixedly attached to the skull, so that in case of need the micromanipulator together with the transducer may be exchanged without disassembly of the mounting means being required. In fact, the removal of the mounting means may require a relatively invasive intervention because the operative access to the fixing screws of the micromanipulator must be exposed. Furthermore it my happen that the respective screw holes in the cranial vault can not be reused because the screws normally are self-cutting and the respective holes in the bone are widened during unscrewing and no longer can provide for an absolutely secure seat of new screws. It may also happen that the “old” access path to the point of aim of the transducer coupling element can be used no longer or only in a very restricted manner. However, the prior solution still leaves much to be desired. Thus, after an exchange of the micromanipulator/transducer unit this unit must be newly adjusted in a troublesome manner in order to exactly align the transducer with the aimed site of stimulation. Thereby the reversion operation becomes distinctly more risky and prolonged, particularly when the transducer postoperatively became defect and therefore an exchange of the transducer is required. In addition it may happen that the intervention, which otherwise possibly could take place under local anesthesia, must be carried out under total anesthesia because the depth and duration of the operation make this necessary. The fixed interconnection between transducer and micromanipulator furthermore involves the technical drawback that it becomes extremely difficult to find a design for both components which avoids left-hand/right-hand differences of the system. This leads to the economical disadvantage that for each new implantation two complete transducer-micromanipulator systems must be delivered because it may be that only shortly before the operation the decision is made together with the patient which side will be operated. Another economical disadvantage is that a reversion operation because of a defect of the transducer requires explantation and throwing away of a fully functioning micromanipulator because the existing laws prohibit a reuse thereof. An other important drawback is that, with the further developments of the electromechanical transducers to be expected, such improved products again can be offered to a patient already wearing an implant merely in the form of a complete exchange of a system involving both the transducer and the micromanipulator.